This invention relates to apparatus for measuring operating parameters of high voltage power conductors and, more particularly, to systems employing sensors which are mounted on overhead power transmission lines for measuring all parameters necessary to monitor operation of single phase circuits, three phase circuits, and an entire electrical power substation. The sensors normally derive their power as a result of current flowing through the power conductor, and the invention further relates to back-up power means for operating the sensors when there is little or no current flow through the conductor.
Various power line sensors have been disclosed in the prior art. For example, the sensors of U.S. Pat. Nos. 3,428,896, 3,633,191, 4,158,810, 4,268,818 and 4,384,289 have been proposed for dynamic line rating of electrical power transmission lines. The power line sensor systems available in the prior art measure certain quantities associated with the operation of an individual overhead conductor, namely, current flow in the conductor, conductor temperature and ambient temperature. The limited information gathered by a single sensor module is transmitted to a local ground station dedicated to that sensor module. Data from various ground receivers is transmitted to a central control station where the information is analyzed.
Sensor modules of the prior art, although providing a means of measuring certain operating parameters of individual conductors, do not provide a means for simultaneous measurement of multiple parameters and communication of data from several sensor modules to a single ground receiving station. Thus, prior art sensors for monitoring transmission lines have not had the capability of simultaneously and accurately measuring voltage, current and phase angle on a single phase or cooperatively on all conductors of a 3-phase circuit. Likewise, prior art systems employing line-mounted sensor modules do not have the capability of measuring and communicating all operating parameters involved in monitoring an entire substation through a single, microprocessor controlled ground station receiving data from a plurality of sensors. It has therefore remained necessary to provide substation monitoring in the conventional manner, i.e., by means of individual current and potential transformers on each conductor at a substation where each transformer is hard-wired to auxiliary transformers on the ground wherein the signals are converted to a level compatible with various transducers. Individual transducers are required to measure each parameter, such as voltage, current, kilowatts. These signals then pass through an array of test switches and terminal blocks which in turn are hard-wired to a Remote Terminal Unit (RTU).
It is a principal object of the present invention to provide a sensor module for mounting directly upon an energized power conductor and capable of measuring simultaneously the voltage, current, frequency, phase angle and other parameters on the associated conductor and communicating the values thereof to a receiving station. The received signals may be further processed to provide other data associated with a single phase or with one or more 3-phase circuits.
It is a further object to provide an integrated system for monitoring parameters associated with operation of an entire electrical power substation using only line-mounted modules, each capable of simultaneously sensing the voltage, current and phase angle on the associated conductor at a predetermined time and communicating the measured quantities to a single ground station microprocessor. The sensor modules, of course, are of a type which may be mounted directly upon energized conductors, requiring no shut down of the circuit during installation. Furthermore, the signals communicated from the modules to the ground station are in a condition for use directly by the microprocessor, thereby eliminating the need for auxiliary transformers, transducers, and the like, necessary for signal conditioning and processing in prior art substation monitoring systems.
Prior art sensor modules, such as the toroidal-shaped modules of previously mentioned U.S. Pat. No. 4,384,289, derive their operating power directly from the conductors upon which they are mounted. Consequently, they are operable only when the line current of the conductor is at or above the minimum value necessary to power the sensor electronics. In a substation monitoring system of the type contemplated by the present invention, it is necessary that the sensor modules also be operable when line currents are below the threshold level, i.e., for monitoring very low current conditions or detection of energized conductors with zero current flow. Therefore, it is an ancillary object of the invention to provide a reliable power back-up system, requiring essentially no removal and/or replacement of batteries for recharging, for operating line-mounted sensor modules.
In a system where a plurality of modules transmit data to a single receiver it is desireable to provide means for insuring that more than one sensor is not transmitting at any given time. It has been proposed to transmit signals in bursts of finite duration at random times, but there is still the possibility that more than one sensor will be transmitting at a given time. It is an additional object of the present invention to provide means for time synchronizing data transmissions from a plurality of sensor modules so that no two modules are transmitting at the same time.
Furthermore, it is an object of the invention to achieve this through self-contained means within each module precluding need for communication between modules or requiring a synchronizing signal from the ground station, called the oombined CRTU.
Other objects, related to the foregoing, will in part be obvious and will in part appear hereinafter.